Decision times of infinite computations

Philipp Schlicht , Philip D Welch, Merlin Carl

Research output: Contribution to journalArticle (Academic Journal)peer-review


The decision time of an infinite time algorithm is the supremum of its halting times over all real inputs. The decision time of a set of reals is the least decision time of an algorithm that decides the set; semidecision times of semidecidable sets are defined similarly. It is not hard to see that ω
1 is the maximal decision time of sets of reals. Our main results determine the supremum of countable decision times as σ and that of countable semidecision times as τ, where σ and τ denote he suprema of Σ1and Σ2- definable ordinals, respectively, over Lω1. We further compute analogous suprema for singletons.

Original languageEnglish
Pages (from-to)197-212
Number of pages16
JournalNotre Dame Journal of Formal Logic
Issue number2
Publication statusPublished - 1 May 2022


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